Such an interferometric measuring device, referred to as a white light interferometer, offers an interferometric measuring method established under the concept of white light interferometry, in which a short-coherent light source is, as a rule, used in conjunction with a Michelson interferometer. In this regard, we refer, for example, to T. Dresel, G. Haeusler and H. Venzke, Applied Optics vol. 31 (1992), page 919, or P. de Groot and L. Deck, “Surface profiling by analysis of white light interferograms in the spatial frequency domain”, Journal of Modern Optics, vol. 42, (1995, pages 389 to 501. In this context, the object is imaged via an objective lens on a CCD camera and superimposed by a flat reference wave. A depth scan of the object surface in the z direction may be carried out as scan of the reference mirror or of the object. In a scan of the object, the image plane of the objective and the reference plane are in the same plane, i.e. the object is only moved in the depth axis relative to the reference plane. In a scan of the reference mirror, on the other hand, only the reference mirror is moved, i.e. the object remains immobile with respect to the objective. In this procedure, the depth measurement range is limited by the depth of field of the objective lens.
A white light interferometer is discussed in German patent document no. 199 48 813 A1 that has an intermediate image of the object in the reference light path. The depth scan, in this context, may be implemented as scan of the reference or as intermediate image scan according to German patent document no. 101 15 524 A1. In a scan of the reference mirror, the reference mirror is moved, i.e. the object remains immobile to the objective. The depth measurement range is limited by the depth of field of the objective lens.
In German patent document no. 101 31 778 A1 a white light interferometer is shown having a panoramic view optical system, i.e. an objective optical system that can take a shot around 360° of a nearly radially symmetrical object region. A depth scan, in this context, may be implemented as scan of the reference or as intermediate image scan according to German patent document no. 101 15 524 A1. In a scan of the reference mirror, the reference mirror is moved here too, i.e. the object remains immobile to the objective in this connection too. The depth measurement range is also limited by the depth of field of the objective lens.
White light interferometers are also known in which a CCD camera may be shifted relative to the ocular lens with the aid of a linear shifting table. This makes it possible to set focusing corrections for different objects or object ranges, in case the object lies wholly or partially outside the depth of field of the objective. However, this solution is comparatively costly from an apparatus point of view, and in addition it is too inflexible when adjusting the focus.
White light interferometry was able to be developed further by the aforementioned techniques altogether in such a way that, for example, valve seats may be measured completely even in narrow and deep bores.
An important requirement remaining with interferometric measuring devices is, above all in connection with measuring narrow and deep bores, to make different objectives and endoscopes at the measuring device easily exchangeable. Besides that, the measuring range is still restricted by the depth of field range of the objective and the optics of the eyepiece. Finally, in special applications, a depth scan may be carried out only as a scan of the reference mirror, since a scan of the object is technically too costly.